The present invention is related to the general surgical repair of separated body tissues, and more particularly to internally fixating and stabilizing such body tissues, specifically bones.
In the present state of the art, there are a number of systems available to repair biological tissues separated in surgery or by injury. These products serve to approximate and stabilize the tissues so that healing may commence and provide compression in the interface to promote healing. Compression and stability are critical for proper anatomical healing of tissue. With the correct amount of compression applied to the interface of the tissue portions to be joined, signals are sent to the tissue, thus allowing the tissue to remodel in proper anatomical position. The amount of compression applied to the tissue interface needs to be appropriate to the type of tissue that is being healed.
Twisted wires are also typically used to keep bone fragments together so they may heal. Twisted wires only hold tension as long as the twisted wire pair remains stable. Often the wires untwist too soon failing to keep the bone fragments together so that they may heal. Wires can also cut into the bone fragments allowing them to separate so that healing is difficult.
When it is necessary to access the thoracic cavity for a medical procedure, for example, it is required to cut the sternum into two pieces using a sternal saw. Once the procedure is completed within the thoracic cavity, the sternum must be repaired. For such repairs, it is known to use a dynamic compression device. Some of the drawbacks of this typical device, and others which are used include:
1. Bulky spring materials, while occupying substantial space, often do not store much energy. Some use polymer elastic bands, while other use coiled springs;
2. Wires are sometimes used to wrap the bones into position in compression with one another. However, wires can have sharp ends that can damage adjunctive tissues. Knot stacks in suture can interfere with the natural movement of surrounding tissues; and
3. Current banding systems that incorporate a biasing mechanism to achieve dynamic compression put the biasing mechanism in line with the band or suture. This practice competes with precious space at the healing site. Suture or bands are used to approximate tissues so that they may heal. It is desirable to obtain the best purchase possible on the tissue, so that the binding mechanics offered by the suture may be utilized. The best purchase is optimized by ensuring that the suture has the greatest contact area with the tissue. If a biasing mechanism is interfering with this concept, the biasing mechanism may diminish the suture's ability to hold the tissues together.
In addition, the current banding systems have stiff bands that are not compliant with bony undulations. Flat sutures are used, but are tedious to tie and do not hold reliably.
Bands address the issues wires have in the following discussion. A band, by definition, is wide. In being wide, a band distributes its forces over a wider surface area. This inhibits the band from digging into the bone. In being wide, a band affords a larger cross-sectional area whereby more material may be realized thus presenting the opportunity to offer as much strength in the construct as is necessary to hold the bone fragments together. As such, bands address wire's two main weaknesses, namely, digging into the bone fragments being held together and, not having sufficient cross sectional area.
Bands bring in other attributes other than strength and reduced pressure on the bone. Some of these attributes are difficult to manage. With strength comes stiffness, as mentioned elsewhere herein. The larger cross-section of the band significantly increases the stiffness of the band. While stiffness and rigidity are good attributes in that they can stabilize the bone union, these attributes can also prevent the band from following the contours of the bone when inserted. This can lead to capturing tissues underneath the band that ultimately destabilize the union as the tissues continue to compress and disappear over time.
Binding the band ends together can also impose some problems. Generally this involves a mechanism on one band end that interfaces with holes or slots or contours on the other band end. This creates a tensioning system that is incremental in nature. As in the twisted wire system, this mechanical interface of the two ends is the weakest link in the system. This mechanical interface becomes stronger as the incremental steps become larger. But larger incremental steps aren't conducive to fine tuning the tension, so this is problematic. Flat sutures have been used to tie tissues together but the residual tension supplied in such a knotted structure is insufficient for optimum healing. There is a lot of fuss/time associated with trying to keep and hold a desirable tension with these flat sutures. What is needed is an attachment means that provides variable tensioning.
Buckles are commonly used to adjust the effective length of a strap or band. Such strap/buckle combinations are commonly used on seatbelts, helmet chin retainers, and shoulder straps. The adjustability of the buckle makes the strap much more functional in these applications. Seatbelts can be adjusted to fit different sized people, helmets can be cinched on tightly and then taken off, and backpacks can be worn by different sized people because the shoulder straps adjust.
There are applications where a buckle may be used in combination with a strap when re-adjustment is not as critical as the first adjustment. This would be an application where the first length adjustment of the strap is critical and closely tied to a specific tension in the strap. Such a feature could add cost and complexity to the buckle. But given the application, the added cost and complexity would be worth its added benefits.
There are many fastener inventions that trade off reversibility of the fastener for functionality. Screws, for example, can attach objects to gypsum board and come out easily if needed. Unfortunately, screws don't hold very well in gypsum board. Toggle bolts don't come out easily, but hold objects rather well to gypsum board. So toggle bolts overcome a screw's lack of holding power in gypsum board at the expense of reversibility.
In the realm of fasteners, screws have insufficient surface area to work well in gypsum board. This deficiency enables the invention of the toggle bolt. This is analogous to the present invention. The common buckle has too much friction in it to be affective in certain applications. A modified version of the same buckle that adds some user complexity and sacrifices the easy re-use of the buckle is preferable in these certain applications.
Consider tying down a cargo load. A strap with a buckle is considered in many cases to not be able to apply sufficient tension to the strap to make the load stable. Many users resort to a complicated ratcheting system that can easily over-tension the load and damage it. Most light cargo loads would benefit from a buckle system that has double the tensioning abilities of the common buckle. This would add some user complexity, but not the user complexity, or cost, realized in a strap ratcheting system.
A low friction buckling system for tying down cargo loads is a re-usable use of this fastener invention. There are, however, single use applications for the invention. Consider straps used for approximating tissues after they have been separated during surgery. A common buckle hardly has the ability to pull the tissue parts together without an external tensioning device. The present modified, low friction buckle invention makes it possible to not only approximate the tissues easier, but to significantly realize more tension in the suture with an external tensioning device.
The low friction buckle systems of the present invention are therefore attractive for use in sternal closure because they offer some distinct advantages over the twisted wires and ordinary buckle systems most commonly used in the procedure.
The present invention thus addresses one or more of the issues discussed above.